1. Field of the Invention
The present invention relates to a write control method for a hard disc drive (HDD), and more particularly, to a method of determining a size of an error generated in a servo sector, a write control method of controlling whether to write data to data sectors successive to the servo sector according to the size of the error generated in the servo sector, a HDD using the method of determining the error size and the write control method, and a recording media for storing computer programs for executing the methods.
2. Description of the Related Art
A hard disc drive (HDD) includes a plurality of magnetic heads respectively associated with rotating discs. Each head writes information by magnetizing a disc surface or reads information by detecting a magnetic field from the disc surface.
Each head is typically assembled with a flexure beam to form an assembly called a head gimbal assembly (HGA). The HGA is assembled with an actuator arm having a voice coil assembled with a magnet assembly. The voice coil and the magnet assembly form a voice coil motor (VCM) that moves the head across the disc by activating the actuator arm.
Information is typically stored on tracks concentrically formed on the disc. The VCM moves the head from a certain track to another track in order to access data stored on the disc surface. Each track contains a plurality of sectors, each sector having at least a servo sector and a data sector.
A servo device of the HDD controls the VCM so that the head follows a desired track. The servo device controls the VCM by calculating a track address and a necessary amount of an offset.
Servo information including a gray code, servo burst signals, etc., is written on the disc by a servo writer and a self-servo writing process when manufacturing the HDD.
As a storage capacity of HDDs has increased, not only a track pitch has become narrower, but also a flying height of the head has become lower. Due to the decrease of the flying height of the head, a margin between the head and the disk has become smaller and thereby a possibility of a scratch to occur on the disc has increased. In the meantime, if polishing of surfaces of the disc is bad or contaminated particles, which are introduced from the outside or produced during operations of the HDD, are placed on the disc, a possibility of a Thermal Asperity (TA), which is caused by contact of the head with protruded particles or contaminated particles, becomes higher.
When the scratch and the TA are generated in the area in which the gray code of the servo information is written, an exact track address cannot be obtained. If a target track and a target sector cannot be followed exactly in a write operation of the HDD, the HDD prohibits data from being written to prevent erasure of adjacent tracks in the first step, performs a write retry, which is a operation to search the target track again or to correct an error while the disc is rotating. Not until the target track and the target sector were searched or the error was corrected, the HDD writes data. If the target track and the target sector are not possible to follow or the error cannot be corrected, the HDD arranges the target track and the target sector to be processed as defected ones, write data on a spare data sector.
FIG. 1 shows servo sectors written on the disc. In a sectored servo manner, servo sectors 102 are disposed on the disc in a radial manner and data sectors 104 disposed between successive servo sectors in a track direction.
FIG. 2 shows a format of servo information written in the servo sector 102. According to the sectored servo manner, generally, servo information includes a servo synchronization signal (SYNC or preamble), a servo index mark (SIM)/a servo address mark (SAM), a gray code, bursts etc.
Among them, the servo synchronization signal has constant amplitude and a constant frequency and serves for providing a clock signal and a gain to be used in reading the servo information. A preamplifier (not shown) sets a clock frequency and an amplifying gain to read the servo information according to the frequency and the amplitude of the servo synchronization signal. The SIM is used to mark the first servo sector among sectors written in a track and the SAM is used to notify a start position of a servo sector. The gray code is used to notify a track address and is set to contribute to increase a writing capacity by minimizing changes in bits between adjacent tracks. For instance, there is only 1 bit difference between gray codes of adjacent tracks. Generally, bursts are used to determine a degree of deviation of the head from a centerline of a track and there are 4 kinds of bursts generally.
FIG. 3 shows a flowchart of a conventional write control method that controls whether to write data on a data sector successive to a target servo sector. Referring to FIG. 3, when a write command is issued, in operation s302 a write retry counter write_retry_cnt is initialized to 0.
In operation s304, it is checked whether an error is generated.
When an error is generated as indicated in operation s304, in operation s306 it is checked if the error is FGRAY (Fault of GRAY), which is an error impossible to correct by an error correction code and related to a gray code.
If the error is not the FGRAY, a write operation of data to a data sector successive to the servo sector (i.e., following the servo sector in an uninterrupted sequence) is allowed.
Otherwise in operation s310 it is checked that the write retry counter write_retry_cnt is less than or equal to a maximum write count max_write_rty_cnt after increasing the write retry counter write_retry_cnt by one in operation s308. If the write retry counter write_retry_cnt is less than or equal to the maximum write count max_write_rty_cnt, in operation s314 a write retry is performed and the process returns to the operation s304. Then, in operation s304, it is checked again whether the FGRAY was generated.
When, it is determined in operation s310 that the write retry counter write_retry_cnt is greater than a maximum write count max_write_rty_cnt that is, the FGRAY cannot be corrected. In operation s312, the target data sector is reassigned, that is, the target data sector is replaced with a spare data sector and data is written to a replaced spare data sector.
In the conventional write control method shown in FIG. 3, if a gray code of the target servo sector is damaged due to a scratch, a TA, etc., the FGRAY can not be corrected, however, the write retry may be repeated. Accordingly, data sectors between a servo sector that has a gray code damaged due to a scratch, a TA, etc., and a successive servo sector are defect-processed. As a result of the defect process, a writing capacity of the disc is reduced by an amount of the defect-processed data sectors, and the spare capacity of the disc is reduced as well.